The present invention relates to an aiming mechanism for a automotive lamp in which a lamp unit can be tilted relative to a lamp housing by turning aiming screws. More particularly, the invention relates to the structure of a nut which is fixedly mounted in a nut insertion hole in the lamp housing to support the aiming screw, as well as to the construction in the vicinity of the nut insertion hole supporting the nut.
FIGS. 6 and 7 show an aiming mechanism for a headlamp of an automobile (such as that disclosed in Japanese Utility Model Unexamined Publication No. 5-23093). A headlamp unit 1 is tiltably supported on a lamp housing 5 by an aiming mechanism composed of two aiming screws 2 and 3, and one ball joint 4. The aiming screws 2 and 3 are threadedly engaged with respective nuts 6, and extend through the lamp housing 5 in a direction generally parallel to the axis of the lamp housing. Each nut 6 is fixedly mounted in a nut insertion hole 5a formed in the lamp housing 5. A ball portion 2a (3a) formed at the front end of the aiming screw 2 (3) is supported by a socket 2b (3b) formed on the lamp unit 1 in a manner so as to allow a pivotal movement therebetween. A ball portion 4a, serving as one member of a ball joint, is supported by a socket 4b, serving as the other member of the ball joint.
When the aiming screw 2 (3) is turned, the aiming screw 2 (3) is moved back and forth relative to the nut 6, so that the socket 2b (3b) moves back and forth together with the aiming screw 2 (3). Namely, the lamp unit 1 is tilted about a horizontal tilt axis Lx and a vertical tilt axis Ly, thereby adjusting the tilt angle of the optical axis L of the headlamp unit 1.
The headlamp unit 1 is supported in a cantilevered fashion by the two aiming screws 2 and 3 extending forwardly from the lamp housing 5 and by the ball joint 4 provided between the lamp housing 5 and the lamp unit 1. With this construction, the weight of the headlamp unit 1 acts on the front end of the aiming screw 2 (3), and thus on the nut insertion hole 5a in which the nut 6, threadedly engaged with the aiming screw 2 (3) is mounted. As a result, the metal aiming screw 2 (3) tends to vibrate or shake relative to the nut insertion hole 5a due to inertial forces acting on the headlamp unit 1 during the operation of the automobile. Also, the nut 6, threadedly engaged with the aiming screw 2 (3), tends to shake relative to the nut insertion hole 5a. In addition, when the aiming screw 2 (3) is turned, it slightly shakes. Therefore, in order to eliminate resulting wear between the nut 6 and the nut insertion hole 5a, as well as between the aiming screw 2 (3) and the nut 6, it is desirable that the aiming screw 2 (3) be supported at a support portion to allow for slight movement so as to prevent stress from developing at the support portion.
For this reason, the nut is made of a synthetic resin more resilient than metal. Generally, however, the lamp housing 5 is also made of a synthetic resin (primarily for the purpose of reducing the weight of the headlamp), and moreover the nut 6 is fixed relative to the nut insertion hole 5a merely by fitting the former into the latter. Therefore, the peripheral edge of the aiming screw-fitting hole of the nut 6 tends to be worn by the shaking motion of the aiming screw 2 (3). Also, the nut 6 can shake in the nut insertion hole 5a causing wear, so that play or backlash develops between the nut 6 and the nut insertion hole 5a. This results in problems that the proper aiming adjustment cannot be achieved and that the supporting of the headlamp unit 1 becomes unstable.